1. Field of the Invention
The present invention relates to an incubator for use in scientific and chemical experiments for incubating bacteria and viruses.
2. Description of the Related Art
An incubator is disclosed in, for example, Japanese Patent Laid-Open Publication No. 3-17121 as a thermostatic cabinet. This thermostatic cabinet comprises a heat insulating box, a storage chamber, a heat insulating outer door, a heat insulating inner door, and a heater. The storage chamber is formed inside the heat insulating box. The outer door and inner door are used to open and close the opening of the storage chamber. The heater is buried in an inner bottom portion of the heat insulating box. The space is formed as a water storage layer. When the heater operates, water in the water storage layer is heated. The inside of the storage chamber is equally heated through the water storage layer. The space between the inner box and the heat insulating box may be an air layer through which the storage chamber is indirectly heated.
The inner box is indirectly heated so that the storage chamber is prevented from being dried. When incubating experiments for bacteria and viruses are performed, high humidity of approximately 98% RH is required. Thus, in such a thermostatic cabinet, a humidifying tray filled with water is disposed on the bottom of the storage chamber. Water is evaporated from the humidifying tray to keep the storage chamber at high humidity.
To keep the temperature in the thermostatic cabinet more equal, heaters should be disposed on, for example, left and right side portions of the heat insulating box as well as its bottom. However, conventionally, the heaters are connected in parallel to an electric circuit that controls their heat generation. In the case that the humidifying tray is disposed on the bottom of the storage chamber, if the temperature and humidity of the storage chamber are lowered due to the opening of the doors, the storage chamber is heated by heat generation (or increase of heat generation) of the heaters. However, before steam is sufficiently produced by the humidifying tray, the temperature of the storage chamber reaches a preset temperature. Thus, the heat generation or the increase of the heat generation by the heaters may be stopped. In this control system, the heat generation of the heater disposed on the insulating box bottom, which directly heats the humidifying tray, is stopped or decreased. Thus, after the doors are opened and closed, the increase of humidity in the storage chamber is delayed, thereby adversely affecting bacteria in the storage chamber.
Even if temperature sensors are disposed at various positions of the storage chamber, since the heat generation of the heaters are controlled in the same manner, the temperature in the storage chamber cannot be precisely controlled.
In addition, in the conventional incubating cabinet, since heaters are mounted to the walls of the heat insulating box and the inner box is heated through the water storage layer or the air layer, heat leaks out from the heat insulating box. Moreover, after the doors are opened and then closed, it takes a long time to restore the preset temperature of the incubating cabinet. During this time, the temperature in the incubating cabinet is unstable.